G E 0 L 0 G I E EN M IJ N B 0 U W - 40e JAARGANG - PAG. 333-346 OKTOBER 1961

DIRECTIONAL EFFECTS OF WINDS, WAVES AND CURRENTS ALONG THE

DUTCH NORm SEA COAST

L. M. ). U. V AN STRAATEN 1

ABSTRACT

As yet very little is known about the movements of sediment along the Dutch North Sea coast. In this paper new data are presented regarding the direCtions in which sediment transport seems to take place. Some of the main conclusions are as follows .

. The directions of Dutch coastal dunes appear to vary wuh a) the primary orientation of the foredunes and b) the relative effect of winds of moderate strengrh blowing from angles that differ from those of the stronger but less frequent winds. The magnitude of this effect depends on the width of the wind-formed de· pressions in the dune areas.

Wave observations show that sand drift must be strong along the northern barrier islands (from west to east), but that its importance must be small along the more south-north directed part of the coast between Katwijk and Texel. This conclusion seems to agree with direct sedimentological evidence.

Comparison of meteorological data with beach measurements between Scheveningeo and Bergen reveals that the relatively frequent westerly and south· westerly winds in the second half of the 19th century resulted in an important (temporary) landward shift of the low tide line. .

CONTENTS

Introduction . . . ... • .. . . . . .. .. .•. .. . . .. ..

Directional effects of winds ... .. .. .•.. ..... Wind directions during the last decennia . .

Direct meteorological observations .. Directions of trees . . . ... ... . . .. .

Dunes .. ..... . ... ... .... . ... .... ..... Dune landscapes . .. .. ... .. . ... . . Age of dunes . .. .. . .. ... . ... ... . .

Dune directions .. .. . . .... . ..•....

INTRODUCTION

333 334 334 334 337 338 338 340 343

The chief agencies influencing sediment tran­sport in the Dutch coastal environments are

1 Geologisch Iostituut, Me!kweg 1, Groningen, Netherlands.

winds, sea currents and waves. These are all vector quantities. To understand the movements of sediment one must therefore be informed not only about their magnitude, but also abou; their directions. The primary aim of the present paper is to review some of the old data and to give some new ones, both with regard to these directions and to the consequences on transport and distribution of sedimencs, especially of the sand.

If the author had limited himself to giving nothing more, he would have had a fairly easy task, and the result would have been a rather short collection of tables and diagrams. But he could not resist the temptation of weaving these data togerher into a more coherent story. By doing so he often had to deal with topics about which very little or nothing is known. A scep­tical reader may t:herefore be less appreciative of the general texture of this paper than of the data which served as the base for it. Never­theless, in irs present shape it may be useful in stressing once again the great lack of data that still exists concerning these problems, the solu­tion of which is not only higly important from the purely scientific point of view, but also from the standpoint of coastal engineering.

Acknowledgements: The writer gratefully acknowledges the help of a considerable number of persons and of several institutions. He is in­debted to the Geological Survey (Haarlem) in general and to Mr. L. A. AE. van Eerde in patticular for making special borirrgs in the Dutch coastal barrier and taking un<l·isrurbed cores and for carrying out gra.nulometric analyses of samples from the North Sea floor. Miss S. Jelgersma, of the same Survey, assisted during the work at sea, while Mr. ]. de Jong skilfully prepared lacquer peels from the cores.

subito e.V. licensed customer copy supplied and printed for Flanders Marine Institute Library (SLI05X00225E)